you could OC the 6850 to something like 4Ghz on air, and burn the Quad sitting at a measily 3Ghz.

umm...no.

Those cpu's are of the same 'fam'...Your 6850 @ 4ghz, would still be a 'slower' cpu, than the Q6600 @ stock. FSB increases for C2D's and Q4's do not give incredible gains in performance...rather, the increases are very small. My CPU @ 4ghz, was still behind in MIPS/MFLOPS when compared to a stock Q6600.

Not to mention the Q6600 can do 3.2ghz+ without effort. There is NO C2D available to match that level of performance...period.